Sharif Digital Repository

This study aims to develop a low computational cost framework to optimize the seismic performance of the steel moment-resisting frames (SMRFs) equipped with friction dampers at different performance levels. To achieve the optimal design of dampers in a structure, a novel approach called adaptive optimisation technique (AOT) is adopted. The basis of this method is to achieve a uniform distribution of damage (UDD) in the structure to exploit the maximum energy dissipation capacity of the dampers. The optimisation objective is to obtain the best position of friction dampers and minimize their slip-threshold force to satisfy a predefined inter-story drift (i.e. selected performance target). The... 

In many earthquake prone regions in developing countries, substandard steel moment resisting frame (SMRF) systems pose a profound danger to people and economy in the case of a strong seismic event. Eccentric bracing systems with replaceable vertical links can be utilized as an efficient and practical seismic retrofitting technique to reduce future earthquake damages to such structures. This paper aims, for the first time, to demonstrate the efficiency of eccentric bracing systems with vertical links as a seismic retrofitting technique for the SMRF structures with WCSB and to develop fragility curves for such structures. To achieve this aim, first, the effect of the vertical links on the... 

Recent studies have indicated the need of considering aftershocks in the seismic design/assessment of structures. This article investigates the effect of sequential mainshock and aftershock earthquakes on eccentrically braced steel frames with vertical energy-absorbing links. To achieve this, 4, 8 and 12-storey frame buildings are modelled in Perform3D® software considering non-linear behaviour of materials and components. The frames are subjected to a set of 12 main earthquake records corresponding to the required hazard level, and then subsequent aftershocks are applied using incremental dynamic analysis (IDA). To reduce the computational cost, an alternative approach is also adopted by... 

The code-based response modification factors are mainly developed based on engineering judgments and experiences from past earthquakes, and hence, they may not lead to reliable solutions considering different performance targets and hazard levels. On the other hand, the uncertainties associated with these proposed values are more significant for new lateral load-carrying systems, such as tunnel-form buildings, due to insufficient information about their performance against seismic events. To address these challenges, this study aims to propose a multi-level approach for the estimation of response modification factors for tunnel-form building structures by taking into account the site... 

In the conventional seismic design methods, heightwise distribution of equivalent seismic loads seems to be related implicitly on the elastic vibration modes. Therefore, the employment of such a load pattern does not guarantee the optimum use of materials in the nonlinear range of behavior. Here a method based on the concept of uniform distribution of deformation is implemented in optimization of the dynamic response of structures subjected to seismic excitation. In this approach, the structural properties are modified so that inefficient material is gradually shifted from strong to weak areas of a structure. It is shown that the seismic performance of such a structure is better than those... 

Recent studies showed that while code-compliant structures can generally protect the safety of the occupants, they may exhibit extensive damages during strong earthquake events. On the other hand, structures are generally designed to satisfy the seismic code requirements with the least initial cost regardless of their life cycle cost. In recent years, value-based design has been considered as an effective alternative for code-based design procedures. In this method, as well as the initial cost of the structure, a comprehensive consequence modeling is performed in the design process. In this paper, for the first time, a value-based design optimization method is developed for seismic... 

A practical optimization method is applied to design nonlinear truss-like structures subjected to seismic excitation. To achieve minimum weight design, inefficient material is gradually shifted from strong parts to weak parts of a structure until a state of uniform deformation prevails. By considering different truss structures, effects of seismic excitation, target ductility and buckling of the compression members on optimum topology are investigated. It is shown that the proposed method could lead to 60% less structural weight compared to optimization methods based on elastic behavior and equivalent static loads, and is efficient at controlling performance parameters under a design... 

In this paper, a practical method is developed for performance-based design of RC structures subjected to seismic excitations. More efficient design is obtained by redistributing material from strong to weak parts of a structure until a state of uniform deformation or damage prevails. By applying the design algorithm on 5, 10 and 15-storey RC frames, the efficiency of the proposed method is initially demonstrated for specific synthetic and real seismic excitations. The results indicate that, for similar structural weight, designed structures experience up to 30% less global damage compared with code-based design frames. The method is then developed to consider multiple performance objectives... 

The vacuum sector of the Brans-Dicke theory is studied from the viewpoint of a non-conformally invariant gravitational model. We show that, this theory can be conformally symmetrized using an appropriate conformal transformation. The resulting theory allows a particle interpretation, and suggests that the quantum aspects of matter may be geometrized  

Laser Powder Bed Fusion (LPBF) technology is a new trend in manufacturing complex geometric structures from metals. This technology allows producing topologically optimized parts for aerospace, medical and industrial sectors where a high performance-to-weight ratio is required. Commonly the feature size for such applications is higher than 300–400 microns. However, for several possible applications of LPBF technology, for example, microfluidic devices, stents for coronary vessels, porous filters, dentistry, etc., a significant increase in the resolution is required. This work is aimed to study the resolution factors of LPBF technology for the manufacturing of superelastic instruments for... 

We propose an effective model for an exponentially expanding universe in the brane-world scenario. The setup consists of a 5D black hole and a brane close to the black hole horizon. In case the brane acquires a specific configuration, which we deduce from stability arguments, the induced metric outside the black hole horizon on the brane becomes de Sitter in static coordinates. Studying the Einstein equations perturbatively we find the effective gravity on the brane at this level and derive the 4D gravitational constant. Considering a homogeneous and isotropic fluid in the corresponding FLRW coordinates we find that the bulk fluid density inside the brane, which has the same equation of... 

Proton exchange membrane fuel cell (PEM-FC) aggregation pressure causes extensive strains in cell segments. The compression of each segment takes place through the cell modeling method. In addition, a very heterogeneous compressive load is produced because of the recurrent channel rib design of the dipole plates, so that while high strains are provided below the rib, the domain continues in its initial uncompressed case under the ducts approximate to it. This leads to significant spatial variations in thermal and electrical connections and contact resistances (both in rib–GDL and membrane–GDL interfaces). Variations in heat, charge, and mass transfer rates within the GDL can affect the... 

Proton exchange membrane fuel cell (PEM-FC) aggregation pressure causes extensive strains in cell segments. The compression of each segment takes place through the cell modeling method. In addition, a very heterogeneous compressive load is produced because of the recurrent channel rib design of the dipole plates, so that while high strains are provided below the rib, the domain continues in its initial uncompressed case under the ducts approximate to it. This leads to significant spatial variations in thermal and electrical connections and contact resistances (both in rib–GDL and membrane–GDL interfaces). Variations in heat, charge, and mass transfer rates within the GDL can affect the... 

Establishing high-quality communication in construction projects is essential to securing successful collaboration and maintaining understanding among project stakeholders. Indeed, poor communication results in low productivity, poor efficiency, and substandard deliverables. While high-quality communication is recognized as contingent on the interpersonal skills of workers, the impacts of communication quality on job performance remain unknown. This study addresses this deficiency by developing a method to evaluate construction workers' communication quality. A literature review is undertaken to capture salient interpersonal skills. Leadership style, listening, team building, and clarifying... 

We present an attempt to improve the performance of multi-class image segmentation systems based on a multilevel description of segments. The multi-class image segmentation system used in this paper marks the segments in an image, describes the segments via multilevel feature vectors and passes the vectors to a multi-class object classifier. The focus of this paper is on the segment description section. We first propose a robust, scale-invariant texture feature set, named directional differences (DDs). This feature is designed by investigating the flaws of conventional texture features. The advantages of DDs are justified both analytically and experimentally. We have conducted several... 

Support Vector Machine (SVM) is a powerful machine-learning tool for pattern recognition, decision making and classification. SVM classifiers outperform other classification technologies in many applications. In this paper, two implementations of SVM classifiers are presented using Logarithmic Number System. In the basic classifier all operations (multiplication, addition and ...) are performed using logarithmic numbers. In the logarithmic domain, multiplication and division can be simply treated as addition or subtraction respectively. The main disadvantage of LNS is the large memory requirement for high precision addition and subtraction. In the improved classifier, multiplication... 

In this study, the essential oil of aerial parts species of a plant called Spearmint was extracted by CO 2 to optimize the results of the supercritical extraction process. In order to achieve maximum total yield extraction and SF-CO 2 concentration, tests were done in a laboratorial pilot considering the Taguchi method under following condition: pressure. 90,100,140,170 bar, temperature. of 35, 40, 45, 50 °C, mean particles size: 250,500,710,1000 μm, flow rate 1,3,5,8 ml/s and dynamic time 30,50,90,120 min. The optimizing conditions for SCE and SF-CO 2 concentration are: 90 bar, 45 °C, 500 μm, 5 ml/s, 120 min and 90 bar, 35 °C, 250 μm, 1 ml/s, 30 min. SCE total yield and CO 2 concentration... 

Processing time and segmentation quality are two main factors in evaluation of image segmentation methods. Oversegmentation is one of the most challenging problems that significantly degrade the segmentation quality. This paper presents a framework for decreasing the oversegmentation rate and improving the processing time. Significant variations in both color and texture spaces are the main reasons that lead to oversegmentation. We exploit Affine Invariant Region Detectors to mark regions with high variations in both color and texture spaces. The results are then utilized to reduce the oversegmentation rate of image segmentation algorithms. The performance of the proposed framework is... 

The remarkable rotational symmetry of the photosynthetic antenna complexes of purple bacteria has long been thought to enhance their light harvesting and excitation energy transport. We study the role of symmetry by modeling hypothetical antennas whose symmetry is broken by altering the orientations of the bacteriochlorophyll pigments. We find that in both LH2 and LH1 complexes, symmetry increases energy transfer rates by enabling the cooperative, coherent process of supertransfer. The enhancement is particularly pronounced in the LH1 complex, whose natural geometry outperforms the average randomized geometry by 5.5 standard deviations, the most significant coherence-related enhancement...